FORCE-GENERATING CAPACITY OF THUMB ADDUCTOR MUSCLES IN THE PARALLEL AND PERPENDICULAR PLANE OF ADDUCTION

The description of thumb movements, especially for adduction at the ca rpometacarpal joint, still gives rise to a confusion among clinicians and researchers. The purpose of this study was to elucidate this confu sion by comparing twitch, tetanic, and voluntary isometric force measu rements of thumb adductors with the thumb positioned perpendicular and parallel to the palm of the hand. Fourteen healthy adult subjects, ag ed between 22 and 40 years, volunteered their participation. Maximum t witch, tetanic, and voluntary contractions were recorded using a strai n-gauge mounted on a wooden platform. Twitch and tetanic contractions were evoked by an electrical stimulator that passed current through su rface electrodes to the skin overlying the ulnar nerve at the wrist. T he results show no statistical difference for the tetanic and voluntar y force measurements between the two planes of adduction (p > 0.5). Th e significant changes observed for the twitch responses between the tw o planes were attributed to a change in the compliance of the muscle-t ransducer unit. To conclude, the present findings provide clinicians a nd researchers with an objective and quantitative basis for assessing the force-generating capacity of thumb adductor muscles in either the parallel or the perpendicular plane of adduction.